1. Field of the Invention
The present invention relates to a telephone apparatus, and, in particular, but not exclusively, to improved on-off control over the power supply of a telephone apparatus which can be arranged at the center oft he steering wheel of a vehicle.
2. DESCRIPTION OF THE RELATED ART
As an example, Japanese Patent Laid-open No. 82541/1986 discloses a telephone apparatus comprised of a mobile radiotelephone incorporated in a vehicle, an operator pad supported at the center of a steering wheel by means of a floating mechanism in a stationary manner irrespective of the rotation of the steering wheel, and an independent handset detachably received by the operator pad. The handset is provided with an independent power supply circuit including a secondary battery cluster, and the pad is provided with a charging circuit for supplying power to the telephone handset power supply circuit. Power is supplied from a vehicle battery to the charging circuit through a slip-ring connector of the floating mechanism. When the handset is placed on the pad, the telephone handset power supply circuit is electrically connected to the charging circuit of the pad, and power is supplied from the vehicle battery to the handset so that the secondary battery cluster is charged. The pad is located at the center of the steering wheel by means of the floating mechanism, and this wheel is adapted to be rotated about the pad. However, since such a telephone apparatus needs a multiplicity of lines such as a power line for supplying power from the vehicle battery to the pad as well as signal lines between the pad and the mobile radiotelephone set (parent telephone set) disposed separately from the pad, it is difficult to arrange almost all of the lines from a steering column cover to the pad by means of wires. For this reasons, the aforementioned Japanese Patent Laid-open No. 83541/1986 proposes that the parent telephone set and the handset are provided with wireless transmitter/receivers, respectively, so that communication can be made between the handset and the parent telephone set by means of their respective wireless transmitter/receivers. A current path which connects the pad through the steering column to the vehicle battery is constituted by a single line with a slip-ring connector, which line is connected to the positive terminal of the vehicle battery voltage. The grounding line of the pad, which is connected to the floating mechanism, is grounded into a vehicle body through the floating mechanism.
The handset is provided with a telephone set power supply switch. When a driver enters to vehicle he turns on the switch and when the driver leaves he turns off the switch.
However, if the driver in the vehicle fails to turn on the power supply switch of the handset, when the parent set calls the handset, the handset does not respond to the call. If the parent set is of a type which has no alarm function, such as a buzzer, for informing the driver of the selection of the handset operation mode, the driver cannot notice the fact that the parent set is calling the handset. If the parent set has an alarm function such as a buzzer which operates even in the handset selection mode, a driver and a passenger inconveniently cannot easily determined whether the parent set of the handset is being called. On the other hand, even when the driver forgets to turn off the power supply switch of the handset and leaves the vehicle, an engine key switch is turned off to stop the supply of power from the vehicle battery to the pad or the handset. Therefore, the vehicle battery is not drained, but the secondary battery cluster within the handset drains. It is a significant waste for the handset to use power when nobody is in the vehicle, and this leas to the deterioration of the secondary battery cluster.